Identifying End of Tx in FTP

[Laris Benkis <lbenkis () bank-banque-canada ca>]

We have a system in place where clients drop off files via FTP to a
wu-ftp server which are then processed automatically by scripts. Files
have to be processed relatively quickly for the application to work
properly therefore the convention we have developed is to indicate end
of transmission by doing a rename of the file once the initial put is done. 
We are trying to tighten the security of the whole process and want to
use FW1 ftp resources to limit where puts can be done.  Unfortunately it
turns out that when the ftp resources are used it is no longer possible to
do rename.  

The question I have then, is anybody doing something similar to this? 
What is a reliable, transparent way to tell that an ftp transmission has
been completed?

We have  a fallback solution where the client would send a file then send
a second delimiter file to indicate that the transmission of the first file is
complete.  This is not desirable as client procedures would have to be
changed.

Any ideas would be appreciated.

Laris